This proposal aims to advance a new understanding of growth factor regulation by colonic microbes. We discovered that Streptococcus gallolyticus subsp. gallolyticus (Sgg), a medically important gut pathobiont, directly activates transforming growth factor b (TGFb) and that this activation is important for the pathogenicity of Sgg. The goal of this proposal is to identify the specific Sgg molecules that mediate TGFb activation. TGFb is a growth factor of fundamental importance. Due to its many functions, TGFb is a crucial player in a range of human diseases (e.g., immune disorders, fibrosis and cancer) and a widely pursued target for therapy. Regulation of TGFb is clearly of critical importance. The mechanisms by which animals regulate TGFb have received intense research attention over the years. In contrast, microbial regulation of TGFb has not been extensively investigated. TGFb is secreted as an inactive latent complex and must undergo extracellular activation to trigger downstream signaling events. To the best of our knowledge, our finding is the first description of a colonic microbe possessing genetically encoded factors for TGFb activation. This is a major breakthrough in the underexplored area of microbial regulation of TGFb and calls for further investigation to delineate the specific Sgg molecules responsible for TGFb activation. The proposed studies further advance the limited knowledge of Sgg pathogenic mechanisms. Our preliminary results along with previously reported in vivo effects of Sgg and the known activities of TGFb strongly support the idea that TGFb activation by Sgg is important for its pathogenicity. Taken together, our findings reveal a novel and clinically important mechanism of TGFb regulation by a colonic pathobiont. Given the importance of TGFb and Sgg, and the current knowledge gap, further investigations to understand the mechanism of TGFb activation by Sgg and the detailed pathobiological consequences of this activation should be of high priority. The primary goal of this proposal is to identify the specific Sgg molecules important for TGFb activation. A combination of genetic, proteomics and biochemical methods will be used to identify the specific Sgg molecules. These studies constitute a critical first step towards filling a major gap in our knowledge regarding regulation of TGFb by colonic microbes in disease. The Sgg molecules identified here will provide vital information and necessary tools for future studies to elucidate the molecular details of this novel and clinically important mechanism and to understand how this activation contributes to the pathogenicity of Sgg and influences the host environment in which it resides. The proposed studies will be carried out in collaboration with Joanne Murphy-Ullrich, University of Alabama at Birmingham.